The invention relates generally to a radar apparatus and a control method of the radar apparatus, in particular, to a radar apparatus capable of detecting an object with the use of a reflected wave from the object such as a vehicle or a stationary body, and a control method of the radar apparatus.
To improve vehicle safety and to realize comfortable driving, there is a call for high performance vehicles. In particular, in order to avoid contact with a preceding vehicle or a pedestrian disposed in the direction of travel, and to perform an automatic driving by following a preceding vehicle, an in-vehicle radar apparatus for detecting these objects is important.
As one of these in-vehicle radar apparatuses, there is a radar apparatus using an FM-CW (frequency-modulated continuous wave) radar system. In the FM-CW radar system, a base band signal with a triangle wave is applied with a voltage controlled oscillator (VCO), is frequency-modulated, and is transmitted ahead of the vehicle from an antenna. In this case, the radar apparatus controls the antenna to scan a predetermined angle area in front of the vehicle and to transmit a plurality of beams to the predetermined angle area at a predetermined interval. In addition, the radar apparatus receives the signal reflected from an object by the antenna, mixes the transmitted signal with the received signal, extracts respective peak signals for an upbeat and a downbeat, groups the respective peak signals, pairs the objects obtained by the grouping, and then calculates a distance and/or a relative velocity between the vehicle and the object (See Patent Document 1).
The radar apparatus disclosed in the patent document 1 predicts the current position of an object depending on the past pathway of the object, groups the peak signals based on the predicted position. By this past corresponding grouping, the radar apparatus is capable of detecting any peak signals even when some peak signals are covered.
In a signal processing device using the FM-CW radar system, when the numbers of the peak frequencies are different from each other for the upbeat and the downbeat, by setting the frequency in which power peaks within the peak width of the missing peak frequency as a peak frequency and setting the peak frequency for the upbeat equal to the peak frequency for the downbeat, the respective peak frequencies are paired therebetween (See Patent Document 2).
Patent Document 1: Japanese Patent Publication No. 2003-149325 A
Patent Document 2: Japanese Patent Publication No. 11-316273 A
However, when an object exists in the vicinity of a stationary body, it is not possible to easily and accurately detect the peak signals corresponding to the object since the peak signals corresponding to the object are covered by the wide skirt of the peak signals corresponding to the stationary body.
An exemplary case where the object exists in the vicinity of the stationary body will be described hereinafter.
FIG. 1A is a diagram illustrating an exemplary actual scene in which an oncoming vehicle 2 is disposed in the vicinity of a stationary body 3 and located in front of a driver's car 1, and FIG. 1B is a diagram illustrating an exemplary detection result thereof. FIG. 2A is a diagram illustrating a map of the peak signals for the upbeat in the FM-CW mode according to FIG. 1A, and FIG. 2B is a diagram illustrating a map of the peak signals for the downbeat in the FM-CW mode according to FIG. 1A.
Under the situation shown in FIG. 1A, a group 100 of beam signals 111 to 115 and a group 120 of beam signals 121 to 123 are formed in the map of the peak signals for the upbeat as shown in FIG. 2A. However, since the peak signals corresponding to the oncoming vehicle 2 are covered by the wide skirt of the peak signals corresponding to the stationary body 3, only one group 130 is formed in the map of the peak signals for the downbeat as shown in FIG. 2B. These events remarkably appear in a case where the reflectivity of the stationary body 3 is large, the maximum peak (for example, the peak signal 113) of the peak signals corresponding to the stationary body 3 is high, the reflectivity of the oncoming vehicle 2 is small due to its stream lined front surface and the maximum peak (for example, the peak signal 122) of the peak signals corresponding to the oncoming vehicle 2 is low.
Generally, in a stationary body determination process, if there is a group of peak signals for the downbeat, corresponding to the maximum peak of the group 100 for the upbeat, the group 110 and the group 130 are identified as the peak signals corresponding to the stationary body, and thus excluded from the other detection processes. Thus, the oncoming vehicle 2 is not identified, and as shown in FIG. 1B, the oncoming vehicle 2 is not detected.
FIG. 3A is a diagram illustrating an exemplary actual scene in which a preceding vehicle 2′ is disposed in the vicinity of a stationary body 3 and located in front of the driver's car 1, and FIG. 3B is a diagram illustrating an exemplary detection result thereof. FIG. 4A is a diagram illustrating a map of the peak signals for the upbeat in the FM-CW mode according to FIG. 3A, and FIG. 4B is a diagram illustrating a map of the peak signals for the downbeat in the FM-CW mode according to FIG. 3A.
In the situation shown in FIG. 3A, a group 210 of beam signals 211 to 215 and a group 220 of beam signals 221 to 223 are formed in the map of the peak signals for the downbeat as shown in FIG. 4B. However, since the peak signals corresponding to the preceding vehicle 2′ are covered by the wide skirt of the peak signals corresponding to the stationary body 3, only one group 230 is formed in the map of the peak signals for the upbeat as shown in FIG. 4A. These events remarkably appear in a case where the reflectivity of the stationary body 3 is large, the maximum peak signal (for example, the peak signal 213) of the peak signals corresponding to the stationary body 3 is high, the reflectivity of the preceding vehicle 2′ is small due to its streamlined rear surface and the maximum peak signal (for example, the peak signal 222) of the peak signals corresponding to the preceding vehicle 2′ is high.
Generally, if there is a group of peak signals for the upbeat corresponding to the maximum peak of the group 210 for the downbeat, the group 210 and the group 230 are identified as the peak signals corresponding to the stationary body, and thus excluded from the detection processes. Thus, the preceding vehicle 2′ is not identified, and as shown in FIG. 3B, the preceding vehicle 2′ is not detected.